1. Field of the Invention
The present invention generally relates to memory storage apparatus. More particularly, the invention concerns an improved memory storage apparatus having a linear actuator for reciprocatably positioning a transducer relative to a disc or other media upon which information is recorded. The actuator is referred to as a linear actuator because it is adapted to move the transducer along a straight line that extends generally radially of the media of the memory storage apparatus.
The present invention provides a linear actuator particularly useful in a magnetic memory storage apparatus of the type known in the art as a Winchester magnetic disc memory storage apparatus. The actuator is situated adjacent the peripheries of several vertically spaced memory storage discs and is designed to rapidly position the transducers to access recorded disc information. The transducers normally comprise floating read/write heads. Although the present invention shall be described in connection with the Winchester disc drive unit, it will be appreciated that the actuator will be useful in other types of electromagnetic memory storage apparatus and will also be useful in optical memory storage apparatus wherein an optical transducer or several optical transducers are incorporated in the actuator.
The need for a compact, high-capacity magnetic disc memory storage apparatus has generated much interest in recent years in the Winchester type of disc drive device. Due to the increased track density made possible by recent developments, there has been an ongoing attempt to provide an actuator capable of extremely rapid access time and yet which is compact. Although some actuators have been generally satisfactory, the known prior actuator designs have not been able to meet most of the following objectives: eliminating carriage thermal expansion causing head misalignment on disc tracks; providing sufficiently high magnetic force constants over essentially the whole stroke length of the actuator to both rapidly accelerate and decelerate the carriage, achieve extremely rapid access times while providing a mechanically stiff carriage and head suspension so that the close loop gain of the servo system can be raised such that the heads do not bounce "off-track" due to forces external to the disc drive; eliminating flexible cable connections to the moving parts; providing a very compact design, particularly in the vertical direction; preventing any magnetic bias force to the carriage bearings; providing that head suspensions do not pass through a magnetic field causing information erasure from the discs; and providing a carriage support and drive arrangement of improved reliability and with components which can be easily be replaced and repaired.
2. Prior Art
Various linear motor-driven disc drive actuators have been suggested in which a single-voice coil is mounted on the rear or side of an actuator carriage which coil upon actuation drives the coil/carriage combination past a series of permanent magnets fixed in a fixed pole piece structure. Typically, these are seen in U.S. Pat. Nos. 3,505,544; 3,656,015; 3,659,124; 3,735,163; 4,287,455; 4,287,794; and 4,305,105. U.S. Pat. No. 4,344,022 discloses spaced coils translatable on the surfaces of two center poles of a pole piece structure past a longitudinal series of fixed magnets of alternating polarity and attached to a carriage which coils and carriage are moved together upon actuation and communation of the coils. None of these patents describe a device that meets the above objectives.